Various types of heart valve prostheses have been developed which operate hemodynamically as a result of the pumping action of the heart. Among the types of heart valves which have been developed are valves having single occluders which pivot along an eccentric axis to open and close the heart valves, such as that described in U.S. Pat. Nos. 4,011,601, 4,423,525 and 4,425,670, and bi-leaflet heart valves, such as those described in U.S. Pat. Nos. 4,484,365 and 4,535,484. The above-mentioned patents illustrate various arrangements for pivotally connecting the valve members or occluders to a valve body and disclose occluders of a variety of shapes. However, most of these designs have never become commercial because of some shortcoming, and the need continues for improved prosthetic heart valves for permanent implantation into the human heart.
In its open position, a prosthetic valve should provide a passageway which is large and which has good flow characteristics so that blood flows freely therethrough without adverse boundary layer separation and with a minimum of drag. The heart valve should be rapidly responsive to blood flow to quickly open during the pumping stroke of the heart and to close quickly when the heart relaxes to prevent substantial regurgitation of the blood. The opening and closing of the valve should be sufficiently soft so that the patient is not disturbed by the sounds produced. The heart valve should be made of biocompatible and thromboresistant materials, such as pyrolytic carbon which is preferred, and in this regard, it is important that all surfaces be well washed by blood to prevent stagnation which might lead to eventual clotting. Furthermore, the action of the valve should be such that it does not cause hemolysis (breaking of blood cells).
Heart valves must be constructed to withstand countless numbers of openings and closings, and wear of the interacting heart valve components thus becomes important. Avoidance of excessive wear at the points which define the pivot axes of the heart valve occluders is of particular importance, and U.S. Pat. No. 4,443,894, issued Apr. 24, 1984, addressed this problem. In the bi-leaflet valve construction shown in that patent, the mounting arrangement was designed so that, in moving toward the closed position, each spherical sector which defined the pivot axis initially moved to the end of a dogleg slot; then, as a part of the seating of the arcuate edges of the leaflets against a sealing lip or seat 26, the spherical sectors are withdrawn slightly from the dead end position. However, not only was such a construction restricted to the closing movement of a pair of valve leaflets, but it was essentially restricted to a construction closely resembling that illustrated. As a result, there was felt to be a continuing need to improve designs to combat wear in heart valves utilizing various types of pivoting occluders.